Welding thick to thin

[mdecamps]

I need to weld some 1/8" wall square tubing to some 1/2" thick steel. I am using a HH175 machine w/.035 wire and C25 gas. I know that a MIG weld can look good, but not penetrate good. My question is how to go about welding two metals of such different thicknesses without burning through one, yet still having penetration on the other. Any help would be appreciated.

Thanks

[Seldom]

Mdecamps
I’m sure there are some great instructors on this site but I’ll try and give you some suggestions.

Because the heavier plate requires more heat in order to achieve fusion then the thinner 1/8” as you said, simply focus your arc/wire primarily on the plate. If the plate is flat and the tubing standing upright, raise your elbow so the wire is directed at the corner but more onto the plate and watch the puddle wash up onto the tubing wall. It’s kind of like the beam of a flashlight. If you want more light (heat) on the plate and less on the tubing raise or lower your elbow- I’m sure you understand the principle I’m fumbling with.

Grind or sand the surfaces to be welded to bright metal.

When in doubt you always can put a little preheat to the ½” plate but usually with ½” it isn’t necessary.

One of the VERY BEST THINGS you or anybody else can do is test yourself with a mock-up of your proposed weldment. If you’ve got some ½” scrap and some 1/8” plate/bar or tubing make a weld (one side of the tube only) and bend it completely onto itself. If your weld or tubing bends and doesn’t break loose from either side without taking base metal with it, you’re good to go! Nothing beats a little confidence booster like proving you can do it before you have to!

About the only way you burn through the 1/8” is if you have a large gap and the heat opens a keyhole.

[chip hayden]

the last two posts have shown concern about penetration and fusion and both have been answered with excellent responses. nothing is a substitute for good welding practices.
however, another option can be considered that i have been using more frequently to remedy the fusion/penetration dilemma. metal cored wire.
higher depositon rates, sprays at lower power,excellent penetration with little chance of melt-thru on thin sections, and fewer passes are usually required which means less distortion.
the only downsides i have found so far are cost and the fuming. i haven't tried different manufacturers yet[i've been using tri-mark], or tried with an inverter[which inherently make less fumes] but i think either or both will cut down on the "smoke". has anyone else found similar results?

[Sberry]

You bring up a point that I hadnt really heard much about here and that is smoke. That was one of the Godsends of going to wire from sticks and I hardly have to ventilate here even in winter when the doors are closed.

[Danco]

are you talking about metal cored or self-shielded? metal cored is a great wire, less fumes than say, dual shield. one thing about it though, its flat and horiz. only. self shielded will give greater penetration than mig wire, but is verrrrry smokey. they are right about the technique......focus heat on larger plate, then "wash" the puddle to the smaller. you wont have to worry about burn through......1/8 is a good thickness.

[chip hayden]

no, i mean metal cored E70C-6. with the reddish tinge on my helme i suspect it's the powdered manganese as it's dispersed across the arc.

[Danco]

i use metal cored in situations where a lot of welding is to be done on thicker materials, and where i can position part to weld in flat/horiz. The beauty of it is no spatter, high deposition rates, and very low fuming. thats why your post confused me.

[chip hayden]

who's wire are you running?

[mdecamps]

This has in no way answered my question because it has gotten way off topic. Should I set the settings more towards the 1/8" or the 1/2" using the 70s6 .035 wire that I am using?

[Danco]

sorry for the metal cored sidebar, however your question was answered.....set for 1/2" and focus heat on larger, while washing puddle into the 1/8. corex is the brand i get.

[Roger]

Torch angle has been talked about.
If your weaving on the 1/8" side of weave no pause but on 1/2" side slight pause to fill in undercut.

[chip hayden]

my apologies also, chip.

[mdecamps]

Thanks guys....that's helpful. Since I have a HH175, then I'll set for 1/4" and spend lots of time on the 1/2" side!